This invention relates to means for reducing launch errors in weapon systems. While the invention is discussed with particular reference to a rocket projectile and its associated launcher tube, those skilled in the art will recognize the wider applicability of the invention to other projectile and launcher vehicle systems.
Unguided projectiles of the prior art for use in air-to-air, air-to-ground, ground-to-ground or ground-to-air modes, generally have been deficient in delivery accuracy. One solution to the delivery accuracy problem is disclosed in the Bauman et al U.S. Pat. No. 3,610,096, issued Oct. 5, 1971. While the prior art in general, and the Bauman et al patent in particular, work well for its intended purpose, at least two error sources affecting the flight of a projectile heretofore have been unresolved.
In order to optimize the accuracy of fin and spin stabilized projectiles, the primary error sources, which include tip off, mal launch, and mal aim errors, must be minimized. The spin and fin stabilized projectile described in the above-referenced Bauman et al U.S. Pat., No. 3,610,096, works well to eliminate tip off error. The structure disclosed in Bauman et al, however, does not prevent the occurrence of mal launch and mal aim errors. Reference may be made to the Bauman et al U.S. Pat., No. 3,610,096, for constructional features not forming a portion of the invention disclosed herein. The invention described hereinafter is compatible with the Bauman invention, and is an improvement of the system there described. Features disclosed in Bauman et al, U.S. Pat. No. 3,610,096 not described herein are intended to be incorporated by reference.
Mal aim error is a term of art having reference to the fact that the center line of the projectile may be directed at some point other than the center line of the launcher vehicle. That is, projectile flight error can arise because of the manufacturing tolerances required in the construction of the projectile and an associated launcher. These tolerances often are sufficient to permit some clearance between a portion of the projectile supports or the projectile itself and the projectile launcher. In effect, the projectile becomes disaligned with respect to the centerline axis of the launcher. Since it is convenient to align any launch platform sight system with the launcher centerline axis, weapon systems have an uncompensated error built into them. Even when extremely close manufacturing tolerances are kept, with resulting increased product cost, the launcher and the projectile often are constructed of dissimilar materials. Consequently, the thermal expansion of the material varies, and again permits the undesirable disalignment between the projectile's centerline and the centerline of the launcher tube.
Mal launch also is a term of art, and broadly refers to errors that may arise from a number of sources. Primarily, this error is a result of the noncoincidence of the projectile's spin axis, which corresponds to the centerline between the centers of the bearings on which a spin stabilized projectile rotates, and the principal axis of the mass of the projectile. Spin stabilization, in itself, is intended to provide some compensation for any nonsymmetrical distribution of the projectile's mass. However, spin stabilization induces mal launch errors when the spin axis and mass axis do not coincide. While the maintanence of extremely high tolerances during projectile manufacture can lessen this error, the degree of accuracy required is such as to be prohibitive commercially.
The invention disclosed hereinafter minimizes these difficulties by providing a projectile having self-contained supports, which supports include integrally formed springs. Upon insertion in a launcher vehicle, the springs isolate the projectile body from the launcher vehicle, and insure that the supports always are in direct contact with the launcher vehicle. Consequently, the projectile body is given some degree of freedom within the launcher vehicle to permit the alignment of the spin and mass axes during projectile spin up but prior to launch while the integral supports necessarily maintain the projectile aligned along the launcher vehicle centerline axis. The forward projectile support preferably takes the form of a journaled aerodynamic fin ring, having a plurality of fins extending radially outwardly from a central hub. The fins contain an open-mouth channel along the distal fin end. The channel has first and second widths with the smaller width portion forming the mouth of the channel and opening through an edge of each of the fin plurality. The channel permits that portion of the fin outboard of the channel to function spring fashion, and the width of the channel mouth is controlled closely so as to limit the possible deflection of the outboard fin portion. The spring rate of the outboard portion of the fin may be controlled by selection of the widths and the lengths of the channel portions. The rearward projectile support is a bearing ring structure forming a part of a flared, aerodynamic skirt and includes a pair of spaced annular members joined by a thin skinned metal membrane. The bearing ring structure functions as a second projectile support during launch, and is frustum shaped in side elevation. The effective I.D. of that portion of the launcher vehicle in which the rearward projectile body part rests is slightly smaller than the effective O.D. of the bearing ring structure. This permits the thin skinned membrane to function as a flexible diaphragm which allows a hoop spring attached to one end of the membrane to stress. The hoop spring thus is able to exert a radial spring force between the projectile and the launch vehicle after projectile insertion. Clearance between the round and the launch tube is thus eliminated, and the round has a predetermined degree of radial freedom within the launcher to permit it to align its spin axis with the principal axis of its mass. Since the projectile is in contact with the launch tube until it is in free flight, and because the mass axis and the spin axis are allowed to coincide, accuracy of the weapons system is improved appreciably.
One of the objects of this invention is to provide a spin and fin stabilized weapon system having improved firing accuracy.
Another object of this invention is to provide a projectile body having integral support means for supporting the projectile in a launcher vehicle, the support means being capable of spring loading the projectile radially in the vehicle.
Another object of this invention is to provide a projectile body having an integrally formed forward support comprising a plurality of aerodynamic fins, individual ones of said fins having spring means integrally formed therein.
Yet another object of this invention is to provide a projectile having a bearing ring mounted along a rearward portion of said projectile, said bearing ring having spring means integrally formed therein.
Other objects will become apparent to those skilled in the art in light of the following description and accompanying drawings.